1. Field of the Invention
The invention relates to a permanent magnetically excited electrical rotary drive for a blood pump and to a blood pump with a rotary drive of this kind.
2. Description of the Prior Art
Blood pumps, which are usually designed as axial or as centrifugal pumps, serve for the forwarding of blood and are used, for example, in the framework of operations on the heart for maintaining the blood circulation. Furthermore, implantable blood pumps are known which are implanted into the body of the patient for the temporary or chronic support of the heart activity.
In blood pumps it must be ensured that no contamination of the forwarded blood arises. Therefore, the rotor of the electromagnetic drive and/or the pump rotor is preferably magnetically journalled in blood pumps. This magnetic journalling of the rotor can be realized either through separate magnetic bearings, that is ones which are different from the drive; or the magnetic journalling is realized through the stator of the drive.
A rotation pump which is suitable as a blood pump and which is designed as a so-called bearingless motor, which means as an electromagnetic rotary drive with a magnetically contactlessly journalled rotor, with no separate magnetic bearings being present for the rotor, is disclosed in WO-A-96/31934. For this, the stator is designed as a bearing and drive stator which comprises a drive winding and a control winding. With these two windings, a magnetic rotary field can be produced which, on the one hand, exerts a torque on the rotor and which, on the other hand, exerts a transverse force on the rotor which can be set as desired so that its radial position can be actively controlled.
Furthermore, blood pumps, in particular in the case of an implantation into the body, should be compact and space saving, but nevertheless achieve a pump performance which corresponds at least to that of the heart. For this it is e.g. proposed in WO-A-96/31934 to provide the rotor of the bearingless motor with vanes so that the rotor of the rotary drive is identical with the pump rotor, that is, forms an integral rotor. This rotor thus serves as a drive rotor, a bearing rotor and a pump rotor, through which a very compact and high performance blood pump can be realized.
Blood pumps are also known in which the pump rotor by means of which the blood is forwarded is different from the rotor of the rotary drive. The pump rotor is designed as a vaned wheel or rotor, which is set into rotation by the rotor of the rotary drive. For this, blood pumps of this kind can be designed, for example, in accordance with the principle of the gap tube motor or of the gap tube pump respectively; or the pump rotor can be magnetically coupled to the rotor of the rotary drive.
An essential importance, in particular in regard to implantable blood pumps, is assumed by the operating reliability. A problem in known rotary drives for blood pumps is that when faults arise, such as, for example, the failure of an amplifier circuit or the breakage of an electrical line in one of the phases of the drive winding of the stator, a correct functioning of the drive is no longer ensured. A failure of the drive of a blood pump resulting therefrom can, however, have very severe, possibly even fatal results. The invention is thus dedicated to the task of significantly reducing this safety risk.